Estradiol activates the genes coding for the oocyte-yolk protein precursor, vitellogenin, in hepatocytes of male and female oviparous vertebrates, while the oocytes themselves are unresponsive to the hormone. The following experimental plan proposes to demonstrate how an artificially introduced functional estrogen binding protein can activate hormone specified, but dormant genes in a non-target cell. The Xenopus oocyte is a convenient non-target cell which is know to supply the factors and cellular machinery necessary to support experimentally manipulated transcription and translation. Microinjection of a crude affinity chromatography purified preparation of Xenopus liver estrogen binding proteins into oocytes resulted in incorporation of 35S-methionine into newly synthesized vitellogenin. These preliminary results suggest that this system can be used to investigate an entire range of questions which remain unsolved in the mechanism of steroid hormone induction of specific gene expression. Further fractionation and reconstitution of the binding protein preparation might define which proteins(s) are essential for initiation and maintenance of transcription. Other questions which could be approached using this system include: what constitutes receptor 'activation' and how is this correlated to the intracellular localization of the receptor, how stringent are the species and hormone specificities for receptors, and which genomic elements interact with estrogen binding proteins or other important regulatory proteins. Eventually it may be possible to use the oocyte as and 'in vivo test tube' providing all nonspecific factors and raw materials for gene expression while all specific factors, both regulatory proteins (including other steroid hormone receptors) and their nucleic acid targets, would be injected into the systems. These kinds of very basic findings are important to the understanding of how steroid hormones activate gene expression in both normal and abnormal growth and development and thus, must precede development of methods for treatment and prevention of cancer, birth defects and other diseases of reproductive tissues.